1. Field of Invention
This invention relates to cardiac assist devices, and more particularly, to a device and method for assisting ventricular output in the human heart.
2. Description of Related Art
During the aging process, weakened or ineffective cardiac muscles may inhibit the cardiac pumping function from either the right, left, or both ventricles. When the pumping activity of the heart cannot meet the body's demands, systemic shock and subsequent organ dysfunction (such as pulmonary edema and renal failure) can result. Weakened heart muscles can also result in an over distended, dilated myocardium, which can have a detrimental effect on the electrical conduction and overall mechanical performance of the heart.
Advances in medical science have attempted to overcome these problems by replacing an impaired heart via heart transplants, or with devices such as artificial hearts. However, heart transplants are difficult to obtain since there is a limited donor supply. Moreover, artificial hearts have proved not entirely effective in duplicating cardiac contractions, are extremely expensive, and are known to be rejected by the human body.
Therefore, rather than replacing the heart, various arrangements have been proposed to assist right and left ventricular output of the existing impaired heart. For example, a number of arrangements are suggested in U.S. Pat. No. 4,621,617 to Sharma (“the '617 patent”). FIG. 1 of the '617 patent proposes an arrangement in which two components are disposed in surrounding relation to the heart and function to compress the heart therebetween to assist ventricular output thereof. The two components are furnished with electromagnetic induction circuitry, numerous pole elements, and are secured to one another by a mechanical hinge. It can be appreciated that the device is quite cumbersome, difficult to implant, and has achieved little if any acceptance. FIG. 4 of the '617 patent illustrates an alternate arrangement in which a compressor element is provided posteriorly to the heart and is movable to compress the heart against the rib cage. This embodiment is somewhat more practical, but nevertheless problematic in a number of respects. For example, no means are provided for evaluating the amount of compressive resistance or intra-cardiac pressure of the heart during compression thereof. As a result, the compressor element may either apply insufficient compressive force to the heart, thereby resulting in ineffective ventricular assist, or apply excessive compressive force, thereby damaging the heart. Additionally, providing a compressor element posteriorly to the heart requires complex surgery in which the entire chest cavity must be opened. Moreover, such placement of the compressor element is largely impractical since the aorta, esophagus and spine are all disposed in close proximity to the posterior portion of the heart and leave little room for insertion of any type of assist device.
U.S. Pat. No. 5,498,228 (“the '228 patent”), which is incorporated herein by reference in its entirety, discloses an electromagnetic biventricular assist device that includes an inductive coil placed on the anterior surface of the chest of a human patient. When the coil receives current, a magnetic field is generated, which repels a magnetic mat that is located on the anterior surface of the heart posteriorly, thereby compressing the heart. These compressions are timed by a cardiogram so as to augment the systolic function of the heart. The morphologies of the electromagnetic field generated by the coil and the magnetic field generated by the magnetic mat are somewhat round. Although the coil is stabilized externally on the anterior surface of the chest, the magnetic mat has the freedom to flip, which would permit opposite poles created by the mat and the coil to attract. However, proper operation of the electromagnetic biventricular assist device of the '228 patent is dependent on like pole interfacing with like pole, so that a force may be exerted on the anterior surface of the heart via the mat, and energy may be transferred to the heart. Therefore, the more consistently a pole generated by the coil can interface with a like pole generated by the mat, the more consistently the device will function properly at the electromagnetic interface.